The overall objective of this project is to evaluate the role of chloride on renin release. In the first year we have demonstrated the following: renin release is inhibited by HCl but not by H2SO4 in rat and dog; potassium depletion prevents inhibition of renin by acute and chronic NaCl loading; inhibition of renin release by NaCl is related to increased Cl- transport in the loop of Henle; in man, renin release is inhibited by NaC1 but not by NaHCO3. These observations are consistent with our hypothesis that the macula densa mechanism for renin release is responsive to alterations of chloride transport in the thick ascending limb of the loop of Henle.